1. Field of the Invention
This invention generally relates to artificial lighting devices which are useful in photographic applications and particularly to a zoom lighting device having optical light control apparatus by which the divergence of a light beam can be selectively changed to illuminate of different rectangular size.
2. Description of the Prior Art
Electronic strobes, flashguns, spotlights, floodlights, and the like are all well-known artificial lighting devices which usually comprise a light source and an associated reflector that cooperate in a well-known manner to project a beam of light within a predetermined solid angle. The solid angle of the projected light beam depends on the reflector shape, the light source geometry, and the position of the light source, usually fixed, relative to the reflector. Thus, a given reflector and light source have the limitation that the light beam therefrom is projected within only one solid angle. Those skilled in the art have recognized this limitation and have provided light control apparatus by which the inherent solid angle of the light beam from such devices can be changed to thereby improve their versatility.
Examples of such prior art optical light control apparatus include diffusion (light scattering) screens as shown and described in U.S. Pat. No. 3,167,256 issued to F. P. Elliot on Jan. 26, 1965 and entitled "Photographic Flash Apparatus" and U.S. Pat. No. 3,860,812 issued to Arthur Schneider on Jan. 14, 1975 and entitled "Diffusion Screen For Photographic Lighting." In Elliot, the patentee shows an electronic strobe adapted to receive a light scattering "lens" that can be manually inserted therein in the path of the strobe light beam to increase the divergence of the light beam emerging therefrom. Schneider also shows a diffusing screen for a similar purpose, but it is not necessary in Schneider to manually change the screen because the diffusion thereof is effected by laterally displacing one optical plate (layer) with respect to another. However, neither of these patents appear to disclose structure for continuously varying the light beam angle of divergence and are thus not as versatile as others which can.
Examples of optical apparatus for selectively controlling the angular spread of a light beam by reducing its inherent angle of divergence are shown and described in U.S. Pat. No. 3,404,612 issued to D. M. Harvey on Oct. 8, 1968 and entitled "Light Regulation Means For Use With Multilamp Flash Units;" U.S. Pat. No. 4,017,727 issued to David J. Tamanoto on Apr. 12, 1977 and entitled "Light Projecting Apparatus;" and U.S. Pat. No. 4,141,059 issued to Shosaki Shiojiri on Feb. 20, 1979 and entitled "Photographic Flash Device." All of these patents in principle use a positive lens, which can be a Fresnel lens, to converge a diverging light beam to thereby reduce its angular spread. This is done by moving the lens axially with respect to the beam. Apparently, relatively large axial displacements are required to effect divergence changes with this type of apparatus and such apparatus tend to be somewhat large and awkward to use.
Another prior art device is described in U.S. Pat. No. 3,484,599 issued to W. D. Little on Jan. 3, 1967 and entitled "Optical Projection Apparatus." Here the patentee shows the use of two spaced apart lenticulated screens mounted for rotation with respect to one another to expand the divergence of a collimated beam from a circular spot to a larger circle of light. In between the small and large circular patterns, the device produces elliptical patterns, but because of this, the device is inefficient for photographic applications requiring the illumination of rectangular formats.
In U.S. Pat. No. 4,101,957 issued to Bansun Chang on July 18, 1978 and entitled "Zoom Operating Light," the patentee discloses an operating light useful in dentistry and medical applications. The size of an illuminated rectangle is changed by imaging it at different magnifications at relatively short conjugates, 13 inches and 32 inches. The areas illuminated are relatively small and therefore would not be suitable for illuminating larger areas commonly found in photographic work. Also, the zoom light disclosed appears to be somewhat large and bulky.
From the foregoing review of the prior art, there can still be seen to exist a need for a versatile artificial lighting device which can provide a light beam whose divergence can be continuously changed in a controllable manner through the use of simplified, compact structure and a primary object of the present invention is to provide such a device.
Another object of the present invention is to provide light controlling structure by which a circular collimated light beam can be continuously expanded to provide generally rectangular illumination patterns at subject distances commonly used in photographic applications.
It is yet another object of the present invention to provide light control apparatus which can effect the foregoing objects with relatively small displacements of its parts.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, the combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.